Pheochromocytomas are neuroendocrine tumors that develop from cells in the adrenal medulla or sympathetic ganglion. Most of these tumors are benign but 10 to 30% are malignant with life expectancy ranging 3 to 5 years. Other than surgery for local disease, there is no known curative treatment for malignant pheochromocytoma. Current therapies for widespread metastatic disease include chemotherapy, chemoembolization, octreotide, and 131I-MIBG. In general these treatments are palliative but very few patients have had complete responses[unreadable] [unreadable] This project tests the efficacy of radiotoxic treatment of malignant pheochromocytoma using 131I-MIBG, and in particular tests whether pre-treatment using specific drugs (so called sentitizers) increases the efficacy of 131I-MIBG treatment. Recently, the protocol has been on hold to find a laboratory that will supply us with 131I-MIBG.